The present disclosure relates to extracorporeal blood circuit devices, and related methods of use. More particularly, it relates to devices for de-aering and oxygenating blood in an extracorporeal blood circuit, along with other possible treatments such as temperature control.
An extracorporeal blood circuit is commonly used during cardiopulmonary bypass to withdraw blood from the venous portion of the patient's circulation system (via a venous cannula) and return the blood to the arterial portion (via an arterial cannula). The extracorporeal blood circuit typically includes a venous drainage line, a venous blood reservoir, a blood pump, an oxygenator, a heat exchanger, one or more filters, and blood transporting tubing, ports, and connection pieces interconnecting the components.
Blood oxygenators are disposable components of extracorporeal circuits and are used to oxygenate blood. In general terms, the oxygenator takes over, either partially or completely, the normal gas exchange function of the patient's lungs. The oxygenator conventionally employs a microporous membrane or bundle comprised of thousands of microporous or semipermeable hollow fibers. Blood flow is directed around the outside surfaces of hollow fibers. Concurrently, an oxygen-rich gas mixture is passed through the fiber lumens. Due to the relatively high concentration of carbon dioxide in the blood arriving from the patient, carbon dioxide is transferred from the blood, diffusing across the microporous fibers and into the passing stream of oxygenating gas. At the same time, oxygen is transferred from the oxygenating gas, diffusing across the fibers and into the blood. The oxygen content of the blood is thereby raised, and the carbon dioxide content is reduced.
Typically, the patient's blood is continuously pumped through the heat exchanger component prior to interfacing with the oxygenator. The heat exchanger core is generally made of a metal or plastic that is able to transfer heat effectively to blood coming into contact with the metal or plastic. With extracorporeal blood circuit applications, the heat exchanger core is normally formed by a series or bundle of capillary tubes. A suitable heat transfer fluid, such as water, is pumped through the heat exchanger core, separate from the blood but in heat transfer relationship therewith. The water is either heated or cooled externally of the heat exchanger, with the heat exchanger functioning to control or adjust a temperature of the blood in a desired direction. After contacting the heat exchanger core, the blood then typically flows to the oxygenator. In fact, many commercially available oxygenator devices integrate a heat exchanger core with a membrane-type oxygenator. With these integrated, combination devices, the oxygenator membrane bundle can be disposed directly over the heat exchanger core's capillary tubes.
Conventionally, the filter device (e.g., an arterial filter) is fluidly connected within the extracorporeal circuit downstream from (or upstream of) the oxygenator, and operates to remove gross air (e.g., air bubbles) and particles on the order of 20-40 microns, as well as trap gaseous microemboli (GME). Known arterial blood filters are available from Medtronic, Inc. under the trade name Affinity® Arterial Filter, and incorporate a membrane or screen filter media with a sufficiently small porosity for capturing GME. The oxygenator and arterial filter devices normally are physically separated components or devices of the circuit.
While implementation of the separate oxygenator and arterial filter devices as part of an extracorporeal blood circuit is well accepted, certain concerns may arise. An arterial filter typically adds 200 mL (or more) of prime volume to the extracorporeal blood circuit; this added prime volume is undesirable as it can lead to increased hemodilution of the patient. As a point of reference, in practice, it is necessary to initially fill the venous and arterial cannulae with the patient's blood and to prime (i.e., completely fill) the extracorporeal blood circuit with a biocompatible prime solution before the arterial line and the venous return lines are coupled to the blood filled cannulae inserted into the patient's arterial and venous systems, respectively. The volume of blood and/or prime solution liquid that is pumped into the extracorporeal blood circuit to “prime” is referred to as the “prime volume”. Typically, the extracorporeal blood circuit is first flushed with CO2 prior to priming. The priming flushes out any extraneous CO2 gas from the extracorporeal blood circuit prior to the introduction of the patient's blood. The larger the prime volume, the greater the amount of prime solution present in the extracorporeal blood circuit that otherwise mixes with the patient's blood. The mixing of the blood and prime solution may cause hemodilution that is disadvantageous and undesirable because the relative concentration of red blood cells must be maintained during the surgical procedure in order to minimize adverse effects to the patient. It is therefore desirable to minimize the extracorporeal blood circuit's prime volume (and thus the required volume of prime solution).
Devices have been proposed that combine or integrate the arterial filter with the oxygenator. Many of these combination-type devices remove air and particles either post-oxygenation phase or integral with the oxygenation phase (e.g., an arterial filter media disposed within a thickness of the oxygenator's wound hollow fiber bundle). In some instances, this may be less than optimal. For example, directing macro air-containing blood through a GME-type filter media during or after the oxygenation phase could allow for the gross or macro air to be “chopped” up into micro air, possibly increasing an amount of the more difficult to remove gaseous microemboli.
With other oxygenator device designs, incoming blood flow is compressed to separate gas from the blood prior to oxygenation. Yet others pass the blood flow through a tortuous path via multiple windows and channels. These approaches may also be problematic. The cells (e.g., red blood cells, white blood cells, platelets) in human blood are delicate and can be traumatized if subjected to shear forces. Therefore, the blood flow velocity inside the oxygenator (as well as other components of the extracorporeal blood circuit) must not be excessive. The configuration in geometry, along with required velocities of the blood, makes some de-aering and oxygenation devices traumatic to the blood and thus unsafe. In addition, the devices may create re-circulations (eddies) or stagnant areas that can lead to clotting. Thus, the configuration and geometry of the various circuit components for a blood flow path is desired to not create re-circulations (eddies) or stagnant areas that can lead to blood clot production.
In light of the above, a need exists for an extracorporeal blood circuit oxygenator device that that combines the attributes of a filter with an oxygenator by affecting de-aering of the blood prior to the oxygenating phase and by filtering particulate, with minimal pressure drop and exposure to shear forces.